Twisted pair communications networks are commonly used to communicate data within a building, or across large distances. In such networks, data is transmitted in the form of a differential signal traveling along a plurality of twisted pair wires within a cable. Current standards for such communication are defined in standards established by the Institute of Electrical and Electronics Engineers (IEEE). Those standards set requirements for frequency and signal amplitude for those differential signals, and are described in IEEE 802.3 standards documentation.
In more recent times, efforts have been made to also transmit power over the cables that contain the twisted pair wires. For example, there are a number of IEEE standards documents within the IEEE 802.3 family that define standards for delivery of power over existing Category-5 (“Cat-5”) or better twisted pair cables. In one configuration defined in the standards, in a Cat-5 or higher cable, a first wire pair will carry differential signals (data) and operate at a first steady state DC voltage, while a second wire pair will carry other differential signals (data) at a second DC voltage. The difference between the DC voltages of the first and second wire pairs provides a DC power source to the far end equipment connected to the Cat-5 cable. In particular, IEEE 802.3af, 802.3at, and 802.3at 4-pair each provide definitions of analogous ways in which a direct current voltage can be delivered on the same wires of a four-pair cable. Equipment supporting this service is referred to as power-over-ethernet, or PoE, equipment, and is compatible with 10Base-T and greater systems, up to systems providing 1 Gigabit data rates. Above that data rate, existing PoE standards do not allow for delivery of power due to interference issues relating to the data passed using higher-frequency differential signals required for communication at those higher rates for S/UTP and U/UTP systems, in which cables generally lack shielding between different differential pairs.
In the existing PoE standards, power and data are integrated on a single cable infrastructure in a way that allows for delivery of power to remote network endpoints, without requiring those endpoints to have a separate AC outlet installation. This provides cost savings, as well as improved safety and network reliability without increasing the complexity of deploying such networks since no additional cabling for power distribution is required. However, existing PoE systems are not without drawbacks. In particular, existing systems that conform to or are compatible with the IEEE standards have limits in terms of the amount of power available to be delivered to the far-end system. In particular, existing PoE systems typically have a 300 milliamp limit, leading to a 17.1 watt maximum power delivery limit per pair at a socket. Practically, PoE systems deliver about 15.4 watts, and under 13 watts are typically assumed to be received due to power dissipation along the line.
Although improved PoE systems (e.g. as defined in IEEE 802.3at-2009), referred to as PoE+, can provide up to 25.5 watts of power, these systems still are generally insufficient to power many types of networking equipment at a far end location, without requiring supplemental power from an AC power outlet. Furthermore, as data speeds increase and cabling requirements move beyond Cat-5 (to Cat-6, Cat 6A, and Cat-7, and beyond, supporting gigabit and 10 G data rates), and corresponding 802.3 standards changes to accommodate higher data rates, there are cases where concurrent power and data are not supported. For example PoE is unsupported for 10 Gigabit applications. As such, existing solutions are limited in terms of both power delivery and capability to continue delivering power as data rates increase.
For these and other reasons, improvements are desirable.